Is the fee for Desktop Events Planner a one-time fee, or, annually, monthly, etc?
The fee for the application is marked as being one time which means that you pay $15 (the price for the application) and then you can use the application for as long as you want or it's supported. I checked the purchase page and there is nowhere specified about recurring payments or something related about it.
Use the following link to reach the page: http://www.mts.net/~jrobert1/dep/download.htm